1. Field of the Invention
The present invention relates to a process for preparing α,α-difluoroamines, difluoromethylene-α,α-diazo compounds and fluorination reagents containing α,α-difluoroamines and/or difluoromethylene-α,α-diazo compounds.
2. Brief Description of the Prior Art
α,α-difluoroamines and difluoromethylene-α,α-diazo compounds have proved to be particularly suitable as reagents for fluorinating alcohols or carbonyl compounds, such as ketones, carboxylic acids and aldehydes. Illustrative thereof is N,N-dimethyl-1,1-difluorobenzylamine which has been used for the fluorination of secondary alcohols and carboxylic acids. However, this method of fluorination is disadvantaged in that it requires, the use of the toxic sulphur tetrafluoride (J. Fluorine Chem. 1983, 23, 219–228).
EP-A 895 991 and EP-A 1 013 629 disclose difluoromethylene-α,α-diazo compounds, in particular 2,2-difluoro-1,3-dimethylimidazolidine, which can be used for fluorinating hydroxyl and carboxyl functions. The preparation is customarily carried out in a two-stage reaction, wherein corresponding urea derivatives are first reacted with a chlorinating agent, and then with ionic fluoride to give the desired products. However, the only moderate yields are obtained here. Illustratively, the chlorine-fluorine exchange only proceeds with a yield of 77% of theory (EP-A 1013 629, p. 145 Example 1).
There is, therefore, a need to provide a process for preparing α,α-difluoroamines and difluoromethylene-α,α-diazo compounds which can be carried out without special safety measures and in high yields.